Posted
by
timothy
on Friday August 05, 2011 @06:50PM
from the easy-enough-kill-all-the-users dept.

bbowman writes "One of my job responsibilities is to set up the small network for our company's exhibit at the trade shows we attend. The mobile demo devices we use depend upon a reliable Wi-Fi connection to a router I have in the exhibit. In the days leading up to the opening of the trade show, W-iFi connections are reliable and work as expected. However, as soon as the show opens none of our devices can reliable maintain a Wi-Fi connection to the router. The devices we use at the trade shows are Windows-based laptops, iPods/iPads, Android tablets, and a variety of Wi-Fi enabled cell phones. I have tried using channels 1, 6, and 11 (as well as the others) and used different routers (Linksys, D-Link, Netgear) without success. I'm sure it is likely that there are poorly insulated electrical cabling, fluorescent lighting, and other issues that would contribute to Wi-Fi interference in the convention hall. A quick scan shows dozens and dozens of discoverable Wi-Fi networks nearby. If I take the router back to my hotel room, I have zero connection problems. How can I overcome this so that Wi-Fi works reliably in the convention hall?"

Then stand up and announce on the loud speaker in a polite English accent to everyone; "So you guys have a choice: Either turn off your Wi-Fi (devices) or I give up. Would you like to see the demos?"......"Then all you bloggers need to turn off your notebooks. Go ahead, just shut the lids. I'll wait," he said.

FYI Steve Jobs routinely uses out of spec channels. For WWDC, this used to be channel 13, which is not licensed for use in the US, but is in Japan.

This got to be a problem (leading to the famous "you've got a choice..." speech) when enough Japanese Mac developers attended without changing their locale, and all the Japanese machines ended up on channel 13 because it was "less crowded" (for obvious reasons).

They use PROTOTYPE equipment all the time... He owns the peeps that can set the channel to whatever Steve wants.

It actually makes sense that Steve would set the network up that way.. It would also keep "nuisance" hackers out of his demo. It does make it extra funny to know Steve was using a channel people in the room should not have been able to access... Not a slightly geeky crowd much?

But on topic, short of having firmware access to unlicensed bands, there's not much you can do. Perhaps conven

13 is allowed in Australia and Europe as well, but overlaps significantly with channel 11 and a few of the other higher channels.There is a channel 14 that is only allowed in Japan and it is far enough above even channel 13 that there's virtually no overlap.http://en.wikipedia.org/wiki/List_of_WLAN_channels [wikipedia.org]

It's not that hard to make a bench top Faraday cage. Just make a wooden frame, and nail some copper mesh all over it. It won't be as good as the professional ones, but it doesn't need to be.

The problem is that people coming by your booth will now see a kludgy mess of wood and wire, instead of your nice, elegant demo.

That is what they see if you build it that way. If you instead put your demo inside a glass or plastic box, with metallic tint coating on the inside and bright lighting inside, they'll see your demo under glass with the sides covered with mirrors. Whether they realize that they're also looking through a mirror is irrelevant.

A Faraday cage to block or strongly reduce 2.4Ghz signals doesn't have to be that ugly, since the allowable size of holes in the mesh is dependent on the wavelength. 2.4Ghz is a wavelength of just under 5 inches. A 2-inch grid could easily be incorporated in to the right kind of industrial-themed decor.

This. Or window screen. Or chicken wire. Or... (It doesn't have to be copper.)

Also, a Faraday cage doesn't have to be small. And the goal is not to create a totally isolated environment, but simply an en

802.11a will get around the interference from other 802.11b/g devices as well as any microwave ovens that might be there, but the real problem might be all of the water interference in the room. Trade shows are full of people, who are full of water, who block your signal.

If the original poster is responsible for the convention center Wi-Fi, what he/she can do is crank down the transmit and receive gain and add more access points. If he/she is a vendor on the trade floor, that might not be enough; if the convention center doesn't set up such high density Wi-Fi for everybody, then every other vendor is going to leave their base station hardware set at the default setting, which, while appropriate for a house in the suburbs, or maybe an apartment complex, is WAY TOO LOUD in a

Alternatively, try renting one of these guys [xirrus.com] and see how you fare. That said, this is probably the Wi-Fi equivalent of a fuel-air bomb, so again, talk to the nearby vendors and try to convince them to share your connection rather than making a further mess of the spectrum.

Its not the vendors. At HIMSS a few years ago we had to go all spy vs. spy to share a single electrical outlet with our booth neighbor. This could have incurred a fine or ejection per the contract with the convention organizer/convention hall.

Finally, you can use a high-gain external directional antenna to provide coverage for just your section of the floor at high enough gain to drown out everybody else (e.g. a 25 dBi yagi pointed down from the ceiling or something). Bear in mind that this is the Wi-Fi equivalent of a tactical nuke, so you should expect retaliation from other vendors the following year....

Maybe.

If the receiving electronics in the mobile devices themselves are already being desensed from all of the local RFI, which may be the re

Actually, it helps a lot. Remember that most traffic is downloading, so the base station statistically does a lot more transmitting than the clients. Even if transmit and receive were equal, though, cutting the shouting in half would still be a big improvement in total noise.

Also, you're forgetting that clients usually reduce their transmit power when possible to maximize battery life. By increasing the station density and lowering the power of the base station, you are significantly reducing the chances

Jumping to the 5GHz spectrum would really be ideal because the problem almost certainly is 2.4GHz band congestion. Unfortunately most of your devices probably won't support the 5GHz band. The ipod touches and the wifi enabled cell phones certainly won't (unless all the cell phones are the Galaxy S2). 802.11n never should have been in the 2.4GHz band and should have been 5GHz only. I'm sure there is some idiot nearby you running a 2.4GHz AP in 802.11n mode, a setting which pretty much takes up the entire

That will block out all the crazies. In this case it needs to be a little bigger than the traditional one. More seriously, I'm guessing that putting your router in an aluminum foil dunce cap above your booth would be sufficient to allow the clients below to connect. Put another router underneath for decoration. You'll have to experiment with how to make it look good but I'm thinking that you could take a cone or hemisphere made with standard lightweight tradeshow construction and cover it with aluminum foil

For the devices that support it (decent laptops, iPad, and possibly other tablets), going to the 5 GHz band is a huge win. There are plenty of non-overlapping channels, and congestion is lower. The problem is that most WiFi enabled phones only support the 2.4 GHz band, so this will not cover all cases.

The problem is intrinsically a hard one, 802.11* wasn't really designed for a zillion flacks in a large room, each toting personal cell routers and whatnot.

However, it is possible that the problem could be solved by money. Let's just say that "(Linksys, D-Link, Netgear)" isn't exactly an honorable lineup of the finest names in Serious Wifi. Cheap, yes, quite delightfully so. Built right down to price? Well, you could say that...

You might want to do some looking into the world of "industrial wifi" products. The environmental resistance of such will be total overkill for a tradeshow floor; but (successful) offerings in that sector are designed for people who need their network to work despite the fact that it is in the middle of a factory floor or next to the arc welder or what have you.

The trouble with going upmarket, though, is that it can be somewhat hard to tell what is genuinely better at wireless networking vs. what is just the same old shit on the wireless side; but in a POE, ruggedized, -40/+135 thermal resistant, with baked-in proprietary management protocols in the firmware, container. You really want the former, not the latter...

Part of that has to do with all the products being fixated on longest distance possible. Which is understandable, but these days one doesn't necessarily want the signal to be that strong as interference with other people's equipment is a much more significant problem than getting a strong enough signal. Whenever I go to set up a new device around here I wind up finding at least a dozen different wireless networks all set up.

It's even worse at a convention like this where you're likely to have even more devi

It doesn't help you much if you don't control most of the devices; but the access points we use at work have a cute little trick where they listen for other APs provisioned from the same controller and automatically adjust output power on some or all of their antennas in an attempt to provide adequate strength, without gaps or areas of unproductive 'shouting', across the entire coverage area(automatically inferred by the APs triangulating one another). We needed denser installations than originally planned

Right, but the standard doesn't really take into account the fact that most of these devices are being used in small spaces. My parents house is only like 25x25 and three stories tall. The furthest distance the signal ever needs to get is like 40 feet or so.

Individuals in condos or apartments likely need even less range than my folks do.

Build your exhibit with a dungeon/prison them to hide the faraday cage that isolates you from the rest of the auditorium. Add lots of dry ice and flashing lights and not only will you have a working exhibit, it will look cool as well.

Even a "cage" that's only on 3 sides (or 4 with a roof) would seriously help. Combine that with the other suggested solutions (using wireless 'a/n', a directional antenna, etc.) should get you enough discrimination that you can get a reasonably clean signal to your devices., If you can choose your booth location so that you can point the 'cage' towards the nearest wall, that would help as well.

In my experience trying to find nice 'free' wireless, I'd also note that I've had my best results with linksys

In the days leading up to the opening of the trade show, W-iFi connections are reliable and work as expected. However, as soon as the show opens none of our devices can reliable maintain a Wi-Fi connection to the router.

I doubt it's this:

I'm sure it is likely that there are poorly insulated electrical cabling, fluorescent lighting, and other issues that would contribute to Wi-Fi interference in the convention hall.

Just an interesting tidbit. I was asked to help out with the soccer game at Qualcomm Stadium last night. They had a special area on the field for the photographers and wanted to be able to have the photographers connected to the net to upload their pictures to their respective news agencies without leaving the field. Just off the tunnel that the players come out is the "media room" where we have just a little Netgear wireless router/access point for the photographers to use during Chargers games, so I just grabbed that, ran 280 ft of CAT-5 out to the field plunked down the Netgear, and set it to WPA2 encryption. I tested it thoroughly the day before the game. The next day, a few minutes after the game started, I got called down to the field because the wireless wasn't working. Everyone was associated with the SSID, but it wouldn't pass any traffic. So I power cycled it, and went back upstairs, and was called back down within minutes. With all the fans in attendance, many of them with wireless enabled smartphones, keeping track of all the wifi in the air must have been too much for the little Netgear, the thing couldn't pass traffic for more than 5 minutes between reboots.

So, plan B, went up to the media booths which weren't really being used for this game, and snagged a crusty old Cisco Aironet 1121B (yes, 802.11b) and put it in place of the Netgear on the field, even left it unsecured as I didn't have time to much about with it. Long story short, not a peep out of it the rest of the game.

I had been told many years ago, that what happens is the mac table of the cheaper wifi gear gets full trying to keep track of all the mac addresses it sees flying around the air, but I haven't confirmed this. Long story short, an old crusty Aironet is better than a fancy new consumer grade AP for large events any day of the year.

The Netgear WNDR3700 is a great router especially when you put DD-WRT firmware on it. DD-WRT made a special firmware JUST for this router which has numerous advanced features. Because it uses the Atheros chipset you can also play with channel size, RTS threshold, etc.

Some Cisco and other high end access points have beamforming networks that can place antenna nulls in directions of interferes (other AP's, microwaves, etc) and point the peak of the beam directly at a user among all types of other fancy tricks.

They work wonderfully well in noisy, cluttered environments. Give them a shot.

My consulting business specializes in providing show management services to associations putting on large meetings. I work with Facilities to provide wifi zones, as well as information kiosks, and internet access kiosks for attendees. I recently did a large meeting in Chicago (30,000+) attendees. This presented many challenges but the biggest issue was on the exhibit floor where a site survey revealed 160 rouge access points on 2.4ghz. Not only was the building Wifi having troubles it was like the wild

Extra points if you bend the aluminium into the shape of a parabola and put the antenna at the focus. That's not as hard as it sounds because a google search will turn up a parabola to print out and use as a template, (or instructions on how to draw one with a compass and ruler which isn't as hard as it sounds). Of course there are other things that can make it better which is why commercial parabolic antennas are often a mesh instead of sheet, but the beer can bent into the right shape would make a diffe

I was thinking that and I'm amazed that nobody had mentioned that earlier. Even relatively big parabolic antennas for WiFi (~1.5metre dish for 2.4GHz or 5GHz) are cheap and there are things like ubiquiti access points that even have much smaller directional antennas as part of the sealed unit.There's a lot of different directional antennas out there.

Sounds like either forcing 801.11n only or using 801.11a is the only inter-operable alternative unless you can modify the devices and play with other parameters.

What about getting the convention hall organizers (or you and your nearby booths) to try and build a mesh, so everybody is on the same network (and can somehow tweak parameters to reduce interference)? Maybe coordinate the channels between nearby booths so they don't overlap? Not that there are than many channels to distribute.

Perhaps the router could be connected to a dish above the booth pointed straight down like a street light. This could overpower other signals in your booth and reduce your interference to other users. Dishes at wifi frequencies aren't large.

I used to set up networks for training and conferences my group did. We picked up an Extricom http://www.extricom.com/ [extricom.com]. I never had problems in the dozen times I used it.
Its an interesting system, it has a central Wifi unit, and you run cat-5 out to 4 remote transmitters. You can place them spread out over the area.
Admittedly the model I used, the Extricom ESX400 and 4 radios no longer seems to be available but check it out.
-Joe

Depends on the physical layout of what you are up to, but directional antennas on the mobile equipment and a 2.4ghz absorbing backdrop behind your stuff might work. Think old Pringles can style directional and a grounded copper mesh covered in cloth for the backdrop.

Take this a step further and run an actual Pringles-can directional. Even if the cantenna doesn't work, the novelty factor of running one, or trying to, in order to overcome the white-noise like interference might draw extra foot traffic. "I see you're rolling bootleg. What else have you got?"

It's likely there's a lot of wifi and other traffic going around. You can probably overcome it with enough gain on the antennas. Directional antennas are best. You can send a beam out that is much higher power than the standard antennas that come with the router. You can go all the way up to dish-style antennas but that is probably going to be rather large and probably overkill.

If you can place routers and access points at multiple locations that would help too.

This doesn't meet the specs of the question, due to the particular devices you wish to support, and the fact that many of them are deliberately incompatible with it.... but there is a technology that I've used successfully many times in the past to overcome the problems inherent and unavoidable in any electromagnetic wireless communication system. This technology dramatically reduces signal attenuation due to distance, it reduces interference from external devices that use the same frequencies, it allows f

i work at a convention hall...are you sure they're not containing your AP? we don't allow outside managed gear although most people don't realize it until they can't connect to their router five feet away. we have our APs contain any rogue APs to avoid losing $$$ to folks showing up and trying to provide free wifi. most of the convention and exhibit centers we deal with do the same thing. the last thing we want is someone providing unsecure free wifi in the building and then we get blamed for 1) shitty bandwidth 2) mitm attacks 3) bad customer service because there's nothing wrong with our gear when you have an issue with dude in the next booth's cell phone tethered AP.

According to this (pdf warning) [arubanetworks.com] what you're calling 'containment' is a 'wireless DoS attack', otherwise known as jamming, and highly illegal. How is Aruba avoiding the wrath of the FCC?

I have been setting up wired and wifi networks in trade shows for 10+ years now.
Welcome to wifi Hell:)

I do not think achieving 100% reliability is a sane goal in that context, but I found that there are simple ways to greatly improve the odds.

> Consumer-grade routers / AP are no good. They often do a fine job, and they always give up quickly.
In my view, using small-business equipment is a better way to go : still affordable, and a lot more resilient.
For about 400 $ you should be able to find a

CSMA (Carrier Sense Multiple Access) makes this a problem. The way this works is the AP and clients listen before transmitting. If they hear another signal above a certain threshold they will try to cooperate by not transmitting until the channel is clear. It's like trying to hold a conversation with a room full of people talking.

5 GHz will probably not work as your client equipment is most likely not equipped with 5GHz capable radios. If they have mini PCI cards you could upgrade them but otherwise your st

Look it up. These things will give you a more focused connection, but you will need setup the antenna correctly for the space you are using. I am assuming you have your wireless router/access point hardwired in your kiosk space. You need to setup 1 or 2 directional antenna and point them (preferably from above) at the area that you have your equipment/devices/demo space. The antenna you use will be dependent on the wireless connection frequency you use (802.11 a/b/g/n 2.4GHz, or 802.11n 5GHz). It will also

Well sort of solved it. We were demo'ing a handheld wireless device that did not have a wired port. We opened the device, popped the nano sized connector from the wifi module to the PCB inverted "F" antenna and connected a very thin coax to the now vacant wifi module's antenna port. We connect all of the unit's coax leads to a RF mixer (think an analog version of a router) and also hooked up a generic wifi router via coax to the mixer so that the handheld units could talk to our on-site server (handheldmixerWiFi routerserver). Our demos worked perfectly. Nobody else had anything working and one of the main points of the show was to show off wifi capabilities. It took a bunch of cables and adapters/gender benders, etc as consumer routers have most of their pin's gender reversed so that you can't do this with retail parts and cables.

Wifi is inherently unregulated. It will have interference and lots of traffic from all the users and devices using the same ISM band. Everything from phones to toys to microwave ovens running in the green room of the booth next door which has a set dressing budget larger than your annual revenue.

You are all unlicensed users and get to accept whatever QoS or lack thereof that you get. There's nobody to whine to, or whine about. It is what it is. On the other hand, there are scary licensed users on that band

Is the problem. It works fine before the show starts and goes to shit after because the AP's are now keeping track of thousands of wandering WiFi enabled cell phones. Consumer grade AP's just can't handle it, some of them will even crash due to their MAC tables filling up (they still have to keep track of MAC addresses even before they authenticate)

In the future, invest $100 in a used Cisco Aironet off ebay. They cost $650 new while your Dlink costs $50 new for a reason.

I have run the networking at several 600-1200 attendee conferences, and have a few things you might want to try...

If any of your devices can use 5.2GHz, make sure you deploy APs for that. 5.2GHz has way more spectrum, and in my experience it tends to work where 2.4GHz is pretty spotty. Try deploying with fairly narrow beam antennas like 90 degrees, so you are just covering your booth, ideally mount it up high looking down. Run at the lowest power setting you can. Use 802.11n equipment, which often see

Since your hardware isn't as flexible as it could be, you can't get away with tricks like special channels and using inbetween spectrum.

So with standard equipment and standard frequencies:1) Use 802.11n, 5 GHz if possible (less crowded)2) Try the wider modes (HT40) to see if they can hop around your interference better (just force it and see what happens)3) Put metal bug screen around the back of your posters and such, (with your AP not behind them). This will decrease sensitivity to whatever is behind your

Reroute the phase coils through the plasma regenerator, then boost the particle stream with a subspace flux inducer. If that doesn't work, try routing your signal through an anti-neutrino pulse, you should be able to generate one by modifying the main deflector.

It's amazing what you can learn about this stuff from a combination of Star Trek reruns and a complete lack of practical experience!

Sorry, no useful advice for your particular situation, but it does remind me that exhibition hall interference is a problem that goes way back.

In the late 80s I worked for an exhibition company and we built a huge pond made up like Portsmouth Docks which ran a couple of remote controlled boats that punters could play with, and were meant to take part in a timed race. (Left unsupervised of course, they much preferred the sport of ramming each other until one sank). The first version used standard 27MHz rad

I wrote code for the 802.11b stack, and have gotten a lot of feedback from the test team as well, and here is my 2c:1. Stacks should handle at least 127 radios on one channel, but most implementations crash with as few as 8 radios alive. Make sure you use a stack that handles many radios. Test your router and your gear (netgear and D-link passed, but check with your current router anyway)2. Nearby channels appear as noise. If you have many TX on nearby channels, you may not have enough signal/noise ratio. M